In conventional wireless network architectures, the radio frequency (RF) connections made between mobile platforms, such as aircraft, and particular RF communication access points disposed about a controlled area, such as at an airfield, is typically accomplished using microwave “line-of-sight” transmissions for modulating data between the aircraft and a ground-based control center in communication with the aircraft. Typically, frequencies in the range of about 2 GHz to about 6 GHz are employed for this purpose. Transmissions at such high frequencies facilitate extremely robust data transmission rates and provide excellent bandwidth for transmitting very large amounts of data very quickly between the aircraft and the ground-based control center. Such high frequency, line-of-sight transmissions are often handled in accordance with well known 802.11a or 802.11b/802.11g communications protocols, although are not necessarily limited to these protocols.
However, a drawback with the use of such high frequency RF transmissions is the limited distance over which such signals may be transmitted. Typically, this distance is about 1000 yards (910 meters) or less for such systems employed at airfields. Thus, when implementing a wireless, high frequency communications system at a controlled area such as an airport or airfield, where runways and taxiways may extend for significant distances and therefore define a relatively large, controlled area, a plurality of antenna substations must be employed. The antenna substations that are intended to communication with the aircraft as the aircraft taxis about the airfield, or is parked at various areas at the airfield for short or long periods, must be sufficient in number and strategically located at those areas around the airfield to ensure that communications can be maintained with an aircraft at all times during which the aircraft is present at the airfield.
With present day airfield traffic management systems the access to the antenna substations is also un-managed. By “un-managed”, it is meant that the decision as to which antenna substation a particular aircraft should communicate which is based upon which antenna substation provides the strongest RF signal to the aircraft, as detected by the RF equipment carried by the aircraft. During situations where many aircraft are accessing the antenna substations simultaneously, this may result in some antenna substations being utilized to capacity while others with a similar coverage area are underutilized, thus leading to network bottlenecks and inefficiency in the communications with the aircraft operating at the airfield or airport. An underlying cause of this problem is the lack of knowledge about each aircraft's position, travel direction and speed, as well as a lack of consideration of the location, antenna type, orientation, and coverage area of the antenna substations.
An additional problem with un-managed, wireless communications systems for managing communications between aircraft and a ground based communications network stems from the transmission delay experienced when the network transfers an aircraft from one antenna substation to another at the airfield. Such delays are often experienced in signal strength based networks as such networks often transfer communications from one antenna substation to another due to the natural signal strength fluctuations experienced with RF transmissions. This can lead to frequent transfers of communication between the aircraft and various antenna substations at the airfield as the aircraft taxies about the airfield. This, in turn, can produce frequent delays in passing important data from the ground based network to the aircraft. With present day systems that rely on signal strength as the means for selecting a particular antenna substation to communicate with, natural signal strength fluctuations can result in the aircraft making and breaking RF connections many times in a very short time period, even while the aircraft is parked at an airfield. This is because with some existing systems at certain airports, an aircraft would be able to detect a beacon signal from several antenna substations simultaneously. The naturally varying signal strengths will prompt the RF communications system on the aircraft to repeatedly make and break communications links with various antenna substations in an effort to maintain communication with the substation providing the strongest beacon signal. Since each interruption in communication can represent a time period of one or more seconds, a large of amount of data transmitted to the aircraft can be lost each time an interruption in the communications link with an aircraft occurs.
Thus, there exists a need for an improved airport traffic management system that is capable of monitoring communications with a large number of aircraft on the ground at an airport and determining the optimal antenna substation to be used by each aircraft, in real time fashion, to even more efficiently manage communications between parked or taxing aircraft at an airport and a ground-based central data network. Specifically, there is a need for a communications system that is able to determine the optimal access point to be used by ground based aircraft, which is not limited to the consideration of the signal strength of received RF beacon signals by the aircraft's RF communications system. This would reduce the frequency of changes by the aircraft in the specific access point with which it is communicating, and therefore reduce the number of instances where communication is lost between the ground based aircraft and the central data network due to the initiation of a new communications link with a different access point. Further, there is a need for a communications system that can monitor and manage the number of aircraft that are communicating with a given access point at a given time to eliminate network bottlenecks and network inefficiencies.
Still another drawback with present day systems is the lack of “scalability” of such systems. Put differently, present day systems are often dedicated to a single airport. Thus, a completely separate control system must be configured at each airport, even if the airports are relatively close in distance to one another. Obviously, this creates significant expense and duplication. It would be highly advantageous if a centralized control system could be implemented that could manage the monitoring and selection of antenna substations for various aircraft at a plurality of independent airports, whether the airports are geographically close to each other or hundreds, or even thousands of miles apart. Such a centralized control system would allow scaling of the capability of the system to accommodate additional airports at a future date. Such a system would also eliminate the duplication of equipment and data that results from maintaining completely independent control systems at each airport that the system is used at.